Renzo Piano Pavilion, Kimbell Art Museum, Fort Worth, Texas

Arup has once again joined forces with Renzo Piano Building Workshop to create a daylighting system within the roof structure to make Piano’s Pavilion an instant classic.

Designed by the Renzo Piano Building Workshop (RPBW) and Kendall/Heaton Associates, the highly anticipated expansion of the Kimbell Art Museum opened late last year to critical acclaim. Subtly echoing Louis I. Kahn’s classic building (with lighting design by Richard Kelly) in height, scale and general layout, the RPBW building has a more open, transparent character. Light, discreet (half the footprint hidden underground), yet with its own character, setting up a dialogue between old and new. A highlight of the design is the top-lit east wing with its innovative light-controlling and power-generating roof system thanks to the work of Arup’s UK office who provided the lighting consultancy services (as well as mechanical and electrical engineering).

Addressing the severe lack of space for the museum’s exhibition and education programmes, the new building provides gallery space for temporary exhibitions, classrooms and studios for the museum’s education department, a large auditorium of 299 seats, an expanded library and underground parking.

The expansion roughly doubles the Museum’s gallery space. The 9,400sqm colonnaded pavilion stands as an expression of simplicity and lightness - glass, concrete and wood - some 60 metres to the west of Kahn’s signature cycloid-vaulted museum of 1972.

The Piano Pavilion is made up of two structures connected by two glazed passageways. The front, or east wing, opens into a glass-enclosed lobby leading to two simply expressed galleries: here, coupled wood beams run north and south, the floors are oak, and the walls are perfect, long expanses of light-grey concrete or curtain glass. The beams support an elegant roof structure of steel and glass, fitted above with louvers that control the flow of sunlight and below with scrims that filter the light before it enters the gallery. As spaces for viewing art, both galleries benefit from the presence of this natural illumination and, through their window walls, from the changing impressions of exterior weather and light. The principal function of the south gallery is to display temporary exhibitions; the north gallery, to show works from the collection.

The West Wing is tucked under an accessible green roof flanked by light wells that allow daylight to spaces below.

Glimpsed from the porch of the Kahn Building, the Piano Pavilion’s east wing conveys an impression of weightlessness: its recessed glass entrance is centered between crisp concrete walls that define the galleries to the north and south; a wafer-thin layer of glass hovers over the heavy steel and wood roof system; and the overhanging coupled wood beams appear to float above the exterior walls.

Approaching the Piano Pavilion, a visitor is aware of its transparency: through the glass lobby the eye moves to the walls of the west wing, sheltered beneath a green roof. Here, in the second of the two structures, unfolds the pavilion’s surprise: an auditorium with bright-red, raked seating plunges below ground to a stage, which itself is set against the backdrop of a deep and broad light well animated by shifting patterns of natural illumination, which shine through the whole structure towards the east.

As always in their museum designs, Piano and Arup continues to experiment with ways to animate and direct natural light, here with a roof system that is notable for its integration of the wood beams as the support for a system of north-opening aluminum louvers and solar cells, mounted above fritted glass and stretched, silk-like scrims.

“The Kahn building is famous for its natural light,” Piano said. “But that was a natural lighting system designed in the late ’60s and ’70s. Technologies have advanced considerably since then. We needed to capitalise on the new technologies and make a design that is more flexible and responsive to the issues of today, like sustainability.” Within and outside the building, they have manipulated light and provided unexpected sightlines by dramatically slanting some of the building’s walls. Canted walls also channel light in two sets of stairwells connecting the upper and lower levels: one leading from the main entrance to the underground garage, and the other descending from the upper level to the lower auditorium entrance.

Arup developed and designed bespoke systems to conserve and display the art in the most appropriate environmental conditions, whilst seeking to reduce carbon emissions.

The roof system above the southeast and northeast gallery and lobby spaces was key to this. A system of motorised photovoltaic louvre elements, constructed from glass and aluminium, generate enough power to offset up to 70 per cent of the carbon emissions relating to the gallery lighting and environmental control systems. The louvres filter daylight to the galleries below and can be adjusted to control daylight levels. This highly integrated design performs three functions in a single element, controlling daylight, excluding direct sunlight and generating power.

“Our collaboration with Renzo began in spring 2007, shortly after he accepted the challenge set by the Kimbell Trustees to construct the extension,” states Arfon Davies, Associate Director of Lighting at Arup.“The client brief was clear, that new galleries were to be daylit, and it was immediately clear that we had a huge challenge responding to what many refer to as the pinnacle of daylight design, sitting just 200 feet away from our project. It was the presence of the Kahn building and its magical use of daylight that formed the first of three ingredients that informed our early daylight design thoughts and discussions.”

The second ingredient was the large body of work they had already created together, especially the museum projects in Texas (the Menil Collection and Cy Twombly Pavilion in Houston and the Nasher Sculpture Centre in Dallas). The brief from Piano to the team was to be inspired by but not restricted by their past work: the solution for the Kimbell project was to be a new chapter and innovation in their 25 year journey of design together.

The third ingredient was the desire to generate a project that minimised carbon emissions and energy consumption. Early studies with the wider Arup design team clearly identified daylight as a key driver to achieving carbon and energy reduction targets.

It was the first ingredient that was focused on initially. What was it about daylighting at the Kimbell that made it so special to so many people? Arup undertook a thorough study and assessment of daylight conditions at the Kahn to understand the quantity and distribution of daylight within the galleries. Interior illuminance levels were logged and High Dynamic Range (HDR) imaging was used to capture daylight conditions at different times of the day, and under different sky conditions.

It quickly became apparent that the quantity of daylight within the Kahn galleries was much lower than was expected; the presence of artificial light in the space is much more. Further study and discussion with the museum also showed that there was a preference for a mix of light, the use of both electric light and daylight at all times, something that low levels of daylight can accommodate.

“The museum was keen to maintain this ability to have a mix of light on objects, with electric lighting being the primary source of light on objects,” recalls Davies.

These early discussions with the museum also showed that there was a keen interest in exploring the potential to make the new building as ‘low carbon’ as possible. Electric lighting is a major source of carbon emissions in most museum buildings. Even with the significant potential of LED light sources, it was found that using daylight as the primary source of light within the galleries for most museum hours, with a minimum electric lighting at these times, would be a major step in reducing the carbon footprint for the new building.

A low carbon strategy encourages the use of daylight over electric light, which leads to a regime where, for much of the year, the art is displayed under natural light alone, and electric light is used only in the winter and towards the end of the day when daylight levels fall.This approach was somewhat different to the existing Kahn building, with relatively low levels of daylight and electric light used during all museum open hours. The museum were keen to maintain the ability to recreate this mix of light – their brief was “The new building should likewise seek to set a new standard in the sensitive use of natural and artificial light in a way that enhances the appreciation of both architecture and art”. At the same time the museum were keen to be as efficient and as low carbon as possible, and to create an exhibition space that can be flexible and adapt its lighting conditions based on exhibition needs. The final brief for the gallery daylight systems was:

• To provide a condition where daylight is the primary source of light for the display of art• To have the ability to tune daylight transmission, and therefore change the mix of daylight and electric light within the gallery.• To be able to reduce daylight levels within the gallery to allow the display of sensitive objects requiring 50 lux or less.• To be able to reduce daylight into the galleries to a minimum when the museum is closed.

To this end, supplementary electric lighting has been delicately combined with daylight within the skylight galleries, ensuring that the correct balance of daylight and electric light can be achieved for all types of art exhibition. All lighting within the gallery spaces is from carefully selected LED sources, a first for the RPBW-Arup team. Using LED lighting within the galleries provides significant energy savings: lighting energy consumption is estimated to be 75% less compared to the existing Kimbell galleries. In fact, the LED lighting, building and system design and photovoltaic power generation reduce the carbon emissions per sqft of the new building to approximately 50% of those from the existing Kahn Building.

Just as Kahn and Kelly made a perfect partnership for the original design back in 1972, Renzo Piano and Arup have created an a scheme for the 21st century. Yes, it is very energy efficient. But it doesn’t achieve this at the expense of great design.

As Piano says: “It is the overall design, as well as the solar technology built into the roof system, that yields important energy savings. This is the way it should be: designing for energy savings is not an ‘add on,’ but, rather, the proper way to build.”

Arup used a three-pronged approach to the control of the Pavilion’s daylighting system.

The need to provide control of daylight levels required the use of a moving, adaptable element in the daylight system. Initial ideas focused on interior motorised louver elements, similar to those used in past projects at the Beyeler and Cy Twombly. This resulted in a system with three layers:

1, Exterior motorised PV louversThis single layer combines four functions in one layer:

The 2,322 extruded aluminium louvers each contains 13 PV cells. 30,186 PV cells in total and aare organised into panels, 6 louvers per panel. One panel is 5’ x 10’. Each individual panel can be individually controlled from the others, and can be organised and grouped together to provide larger areas of dedicated control e.g. a 40’ x 40’ gallery space with different daylight conditions to the remainder of the gallery.The louvers have a number of pre-set positions:

The louvers are controlled by a custom designed web interface, which automatically position them based on timeclock events moving twice a day, once when the museum opens to a pre-set position, and once to a fully closed position once the museum is closed.

The louvers are not actively controlled. They do not try and respond to changing daylight conditions based on photocell measurements. This is intentional as it was desired to keep the variability of daylight, in a similar way to what is experienced in the Kahn building.

The museum have a lookup table, which allows them on a month by month basis to select the appropriate louver open angle when the museum is open, and based on the exhibition requirements.

2, Curved double glazed skylight glassKrypton-filled with PVB laminations to filter out harmful UV radiation. The glass has a low-e coating on surface 2, an acid etch on surface 3, and a simulated acid etch frit on surface 6. The etching treatments were extensively tested to provide some diffusion, whilst maintaining some view of the louvers above.3, Fabric scrim panelsPanels span the entire 40m length of the gallery space, provide final diffusion of light. The material is a custom woven fabric material consisting of 100% Trevira CS yarn, selected to provide transparency to allow visitors to read the volume above the fabric ceiling.